For avoiding duplicate user defined object we need to implement the hashCode and equals method
import java.util.HashSet;
import java.util.Set;
class Employee
{
int id;
String name;
Employee(int id,String name)
{
this.id=id;
this.name=name;
}
public int getId()
{
return id;
}
public String getName()
{
return name;
}
public int hashCode()
{
System.out.println("In hashcode");
int hashcode = 0;
hashcode = id*3; //use any prime number
hashcode += name.hashCode();
return hashcode;
}
public boolean equals(Object obj)
{
System.out.println("In equals");
if (obj instanceof Employee)
{
Employee e = (Employee) obj;
return (e.name.equals(this.name) && e.id == this.id);
}
else
{
return false;
}
}
}
public class HelloWorld
{
public static void main(String []args){
Employee e1=new Employee(1,"Ramesh");
Employee e2=new Employee(1,"Ramesh");
Set<Employee> set=new HashSet<Employee>();
set.add(e1);
set.add(e2);
System.out.println("Size = "+set.size());
}
}
***
Suppose we want to add object based on name only -
Employee e1=new Employee(1,"Ramesh");
Employee e2=new Employee(2,"Ramesh");
Here name is same but id is different so how we will avoid this type of duplicate object based on name -
Only hashCode and equals method need to update-
public int hashCode()
{
System.out.println("In hashcode");
int hashcode = 0;
// only name hashCode require
hashcode += name.hashCode();
return hashcode;
}
public boolean equals(Object obj)
{
System.out.println("In equals");
if (obj instanceof Employee)
{
Employee e = (Employee) obj;
return (e.name.equals(this.name)); // no need to compare id
}
else
{
return false;
}
}
